GROWTH VARIABLES AND WEIBULL DIAMETER DISTRIBUTION MODELS FOR MANGROVE SPECIES IN FORESTRY RESEARCH INSTITUTE OF NIGERIA,ONNE, RIVERS STATE,

Abstract

1. Identification and estimation of quantitative variables of tree stands are basic requirements for forest
   planning, management and production. This study was conducted to assess the growth variables and
   diameter distribution models of mangrove species in swamp forest of Onne and to ascertain the best
   fitting models using Weibull diameter distribution. Systematic sampling technique was employed for
   plot location. The design used four – 10m x 20m rectangular plots laid along four 100m transects at
   intervals of 10m; with 5 x 5m sub-plots nested within them and in an alternate manner. All mangrove
   trees with diameter > 10cm were measured in the entire plots while on the 5 x 5m sub-plots, all trees
   with diameter < 10cm and height > 1.3m were measured. The mangrove species composition in the
   study zone revealed 231 mangrove tree stands belonging to two families namely: Rhizophoraceace and
   Avicenniaceace. Species richness of the mangrove species in the study area shows that Rhizophora
   racemosa were the most abundant with 212 stands and 0.073m3 of volume, followed by Avicennia
   germinans and Rhizophora mangle. The Rhizophoraceace was the most prevalent family, while low
   diversity of some families may be attributed to natural competition. There were strong correlations among the species growth parameters with significant correlation coefficients at P<0.05. The goodness
   of fit for the mangrove species revealed that Kolmogorov Smirnov (Ks) had the better ranking followed by Anderson Darling (HA) and Chi-Squared (R
   2
   ). This is indicative of plausible potential of Weibull
   diameter probability distribution function (PDF) in fitting diameter classes for sustainable management
   of mangrove ecosystem.